The disclosed technology relates to a lubricant for a sump-lubricated internal combustion engine, especially such an engine that is fueled by natural gas. In certain embodiments the same lubricant is also used to lubricate a compressor that is driven by the engine.
Internal combustion engines may be fueled by a variety of liquid or gaseous fuels, including natural gas. While liquefied natural gas or compressed natural gas may sometimes be used to fuel small engines on vehicles, more typically natural gas is used to power large “stationary gas” engines that may be fueled by natural gas supplied directly from a gas wellhead, with minimal or no purification prior to consumption by the engine. Such gas may contain certain amounts of condensable hydrocarbons such as propane, butane, or heavier hydrocarbons, as well as water.
Natural gas engines are known and are described, for instance, in U.S. Pat. No. 8,288,326, Tobias et al., Oct. 16, 2012 (also published as WO 2001/028751, Mar. 10, 2011). The severe operating conditions and demands placed on a lubricant in such engines are described in paragraphs 0004 through 0010.
Stationary natural gas engines may be used to provide power to a variety of devices such as machinery, generators, or compressors. In certain embodiments, compressors powered thereby may be used to compress the natural gas itself. That is, natural gas derived from the wellhead may be divided into two streams, one of which is used to fuel the engine, and another is fed to a compressor, which may be a multiple-stage compressor. The resulting compressed gas may be used for any of a variety of purposes and delivered in a variety of ways, e.g., transportation via pipeline or storage in a receptacle for subsequent use or transportation. In some instances, the compressed gas may be injected into the ground at high pressure in order to facilitate recovery of petroleum from a well.
A natural gas compressor is typically a multi-stage screw compressor or a multi-stage reciprocating compressor, either of which may be lubricated by a lubricant supplied from a sump. Each stage of the compressor will typically be associated with one or more scrubbers to remove contaminants such as water or condensable hydrocarbons that may condense, e.g., after a previous compression and/or cooling stage. Such scrubbing is designed to not only remove contaminants from the final condensed gas stream, but also to prevent contaminants from fouling various components of the compressor and related equipment (such as valves, metering devices, pumps, and gears).
Both the stationary natural gas engine and a compressor powered thereby require lubrication, and it is found to be convenient in some instances to use the same lubricant for both pieces of equipment. This dual usage creates unusual demands on the lubricant, since the conditions encountered in an internal combustion engine may be quite different from those in a compressor. In particular, an engine lubricant will typically be exposed to a very harsh environment in terms of oxidation and nitration and consequently will be formulated to include high levels of high-soap detergents and antioxidants. A compressor, on the other hand, will typically involve the interaction of the lubricant with the hydrocarbons and other gaseous and liquefiable components of the natural gas, and compatibility therewith is required. In particular, a problem is sometimes observed in that water-containing condensate in a scrubber may mix with small amounts of lubricant oil (used for both the engine and the compressor) and may form an emulsion. This may lead to foaming and or plugging of lines and valves such as scrubber dump valves, as well as contamination of the lubricant itself and consequent deterioration in performance. It is desired to minimize or eliminate emulsion formation in such systems. Moreover, in the lubrication of stationary gas engines, with or without an associated compressor, it is desirable to provide a lubricant which reduces or eliminates combustion chamber (i.e., cylinder head and/or piston crown) deposits and reduces copper corrosion. A desirable lubricant may also exhibit good retention of basicity during use (as measured by retention of TBN) and slowed increase of acidity (as measured by retaining a low value of TAN).
Some or all of these benefits are provided by the lubricant of the disclosed technology.
PCT publication WO 2012/097026, Vilardo et al., Jul. 19, 2012, discloses a method for lubricating a sump-lubricated, spark-ignited engine comprising supplying to said engine a lubricant which comprises (a) an oil of lubricating viscosity; (b) a polyether fluidizer; and (c) a metal-containing detergent; said lubricant having a total phosphorus content of less than 0.06 percent by weight.
U.S. Pat. No. 3,933,662, Lowe, Jan. 20, 1976, discloses polyalkoxylated compounds combined with alkaline earth metal carbonates dispersed in a hydrocarbon medium to provide lubricating compositions of superior acid neutralizing capability and rust inhibition in internal combustion engines. Other additives may be present including ashless dispersants such as succinimides. The internal combustion engine tested is a Sequence IIB engine.
U.S. Pat. No. 6,001,780, Ho et al., Dec. 14, 1999, discloses ashless lubricating oil formulation for natural gas engines. Included is an untreated polyalkylene or polyalkenyl succinimide dispersant and a borated succinimide dispersant. The polyalkylene or polyalkenyl group may be derived from polyisobutene and may contain at least about 20 wt. % of a methylvinylidene isomer. Among other additive components are demulsifiers such as polyoxyethylene alkyl ether; rust inhibitors may also be nonionic polyoxyethylene surface active agents.
U.S. Publication 2006-0166843, Rajewski et al., Jul. 27, 2006, disclose polymeric additives for compressor lubricants that can reduce the amount of lubricant carryover as mist in compressed gas from the discharge side of the compressor. Optional lubricants include dispersants, detergents, corrosion inhibitors, etc. The lubricant may contain a carboxylate ester, polyalkylene glycol.
U.S. Publication 2007-0142239, Boffa et al., Jun. 21, 2007, discloses a method for reducing catalyst poisoning in exhaust after treatment systems. The lubricant may contain overbased detergent and succinimides and contains no more than 0.12 weight percent phosphorus. Rust inhibitors include nonionic polyoxyethylene surface active agents; metal deactivators include triazole derivatives; demulsifiers include polyoxyethylene alkyl ether; foam inhibitors include alkyl methacrylate polymers.
U.S. Publication 2012-0132166, Andoh et al., May 31, 2012, discloses a lubricating composition for automotive engines containing a nitrogen-containing ashless dispersant, an alkaline earth metal-containing detergent, and other components. Auxiliary additives include benzotriazol compounds, . . . nonionic polyoxyalkylene surface active agents such as . . . copolymers of ethylene oxide and propylene oxide functioning as rust inhibitor and anti-emulsifying agent. In an example, a dispersant is prepared by thermally reacting a highly reactive polyisobutene containing at least approx. 50% of methylvinylidene structure with maleic anhydride.
WO 2012/03537, Greaves et al., Mar. 8, 2012, discloses corrosion inhibiting polyalkylene glycol-based lubricant compositions for use in extreme conditions such as those experienced in wind turbine gearboxes. The lubricant may comprise, among other components, a random or block copolymer polyalkylene glycol based on ethylene oxide and propylene oxide; a polyalkylene [sic] homopolymer having propylene oxide or butylene oxide units. It may contain a yellow metal passivator which may be, e.g., tolutriazole. It may contain a corrosion inhibitor such as an alkenyl succinic acid half ester in mineral oil.